1. Field of the Invention
The present invention relates generally to a wiring arrangement, and more particularly to electrode wiring on a mounting substrate adapted for use in liquid crystal display apparatus, the electrode wiring including portions of Mo or Mo alloy to which bumps of an integrated circuit such as an LSI are connected.
2. Description of the Prior Art
As a method of mounting an integrated circuit (IC) or the like on a substrate, a direct bonding in which IC chips are connected face-down to a substrate is well known. In this method, tiny electrodes formed on the IC chips are connected to electrodes on the mounting substrate with conductive paste, etc. This method is particularly suitable when a large scale integration (LSI) with high integration is mounted on the mounting substrate.
For connection convenience, electrodes of ICs are projected, which are commonly called bumps, and those projected on the mounting substrate connected to the bumps are called pads because of their pad-like nature. A number of circuit pattern wirings are electrically connected to the pads on the mounting substrate.
Japanese Laid-Open Patent Publication No. 60-238817 discloses a method of mounting ICs or the like for driving a liquid crystal by using a glass substrate of a liquid crystal panel as a mounting substrate in the above-mentioned manner. This method makes possible a direct mounting of an IC on the panel for driving a liquid crystal, an LSI, or the like, with the use of an increasing number of pins depending upon a magnification, a high definition, and a minimization of picture element pitches of a liquid crystal display apparatus. This method uses pads made of Au or ITO (Indium Tin Oxide).
However, the above-mentioned known method has the following problems:
When the pad is made of Au, the connection resistance at a connecting portion between the bumps and pads is low and stable. The formation of such a pad requires a gilding process, thereby complicating the step. In addition, Au is expensive, and the production cost becomes high.
When the pads are made of ITO, it is advantageous in that the process of making them can share the process of making transparent electrodes of ITO during the production of a liquid crystal display panel, thereby reducing the number of steps in the process. However, there is a problem that the connection resistance at the connection points between the pad made of ITO and bumps becomes high (5-10.OMEGA.). When the connection resistance increases, the voltage applied to the liquid crystal display portion substantially decreases due to a voltage drop at the connection points, so that the quality of the resulting display becomes poor. This is particularly notable in a large-sized or highly definitive liquid crystal display apparatus. These display apparatus generate a number of outputs per IC so as to drive a liquid crystal with high clock frequency, and a greater power consumption in the ICs and a liquid crystal itself, so that instantaneous passage of a current is difficult through the circuit patterns. This causes a further drop of the voltage applied to the liquid crystal display portion.